At the beginning of the Chinese Lunar New Year, the millennium-old Mogao Grottoes, a UNESCO World Heritage Site in Dunhuang in northwest China's Gansu Province, have seen an endless stream of tourists.

Dating back to the 4th century, the cave temple complex was excavated in 10 dynasties. The site, where more than 60,000 cultural relics have been unearthed, features 735 caves carved into a cliff, and currently houses 45,000 square meters of mural.

Being surrounded by a vast desert, the Mogao Grottoes had been severely impacted due to wind and sand nearly a century ago. Consequently, Chinese researchers have made continuous efforts to combat sandstorms, mitigate disasters and digitally preserve the murals, employing scientific and technological methods to ensure the grottoes remain vibrant and well-preserved.

Workers had to clean 3,000 to 4,000 cubic meters of sand per year at the very beginning, otherwise, the murals and colored sculptures would be polluted and eroded by wind and sand. The initial manual efforts included building walls and fences and digging ditches to transport sand.

During the late 1980s, scientific techniques were used to manage wind and sand, which included the construction of automatic weather stations atop the caves. These stations were tasked with conducting continuous monitoring of the local environment, particularly focusing on wind conditions by pinpointing the source and movement patterns of sand.

In 2011, a project to prevent and control wind and sand in the Mogao Grottoes was completed, with an investment of nearly 14 million yuan (about 1.95 million U.S. dollars). As part of this project, grass grid sand barriers, covering an area of 1.14 million square meters, and nylon net fences measuring 6,000 meters in length were installed.

Monitoring data showed that the project has effectively decreased the annual inflow of sand into the caves by 85 percent.

Additionally, more than 600 sensors have been installed in the grottoes to monitor information like temperature, humidity, carbon dioxide concentration and passenger flow for disaster prevention.

"If the monitoring data exceeds the prewarning value, we will halt the opening of caves at risk and implement natural ventilation measures to safeguard them to the maximum possible extent," said Chai Pengfei, a staff member of the Dunhuang Academy.

While achieving fruitful outcomes in safeguarding the Mogao Grottoes, cultural relics experts at the Dunhuang Academy have also devised methods to create a digital replica, ensuring the permanent preservation of these invaluable colored sculptures and murals.

Since the late 1980s, they began photographing the murals and subsequently pieced these photographs into comprehensive digital representations of the murals using computers.

"We need to take thousands of photos for a mural covering some 10 square meters. The digitized product is four times the size and looks much clearer on the screen than in the cave," said Yu Tianxiu, director of the Dunhuang Academy's cultural relic digitalization institute.

However, the workers faced challenges in maneuvering freely to capture photographs within the confined spaces of the narrow grottoes while ensuring the preservation of the cultural relics. As a result, the digitalization process took some 20 years from the initial ideation.

With the advent of 3D laser scanning technology, data acquisition efficiency at Mogao Grottoes has been significantly enhanced in recent years, with image accuracy improving from 75 dots per inch (DPI) to 300 DPI. Experts can now take pictures of 20 to 30 caves each year, compared with only one or two caves annually earlier.

By the end of 2022, the Dunhuang Academy had completed the digital photography collection of 289 caves, along with the 3D reconstruction of 45 colored sculptures and 140 caves.

These precious digital works have been disseminated worldwide. In 2022, an official blockchain-based platform was launched, making over 6,500 high-definition digital archives accessible to the public.

"In the past, cultural relics workers at Dunhuang had to use ladders and rely on flashlights, and sometimes even telescopes, to observe the murals. But today, scholars and culture enthusiasts across the globe can access these images from their homes with just a click of the mouse," Yu said. 

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